Spatial distribution of α-elements in CALIFA galaxies
IDPASC Portugal - PHD Programme 2016
2016 / 2017
Jean Michel Gomes
Universidade do Porto
Instituto de Astrofísica e Ciências do Espaço, CAUP
A long-standing puzzle in extragalactic research is the anomalous abundances of so-called α-elements (e.g., C, N, O, Ne, Si, S, Mg and Na) relative to iron (Fe) in early-type galaxies (ETGs). These elements are generally enhanced relative to Fe by an "enhanced-ratio" [E/Fe] correlating with the stellar velocity dispersion (hence, the total stellar mass) of an ETG. The dominant physical mechanism responsible for this trend is still unknown yet fundamental to the understanding of the chemo-dynamical evolution of ETGs across their entire mass spectrum. Three main scenarios have been proposed for these discrepancies: a) a varying star-formation rate efficiency in massive ETGs, b) a non-universality of the stellar initial mass function (IMF) in the sense of a "top-heavy" IMF and c) selective loss of elements due to galactic winds. All these scenarios attempt reproducing the observed [E/Fe] ratios as essentially the result of chemical enrichment by Type II and Type Ia Supernovae, each acting on different timescales, and with a relative frequency closely linked to the galaxy star formation history. Studies of stellar populations in galaxies have dramatically advanced in the last decade. Instead of using a few hand-picked Lick indices, fluxes and integral colours to constrain the star formation- and chemical enrichment history of galaxies, modern spectral synthesis codes and computing facilities now permit a detailed modelling of the full optical spectrum of a galaxy in a pixel-by-pixel approach. These modelling tools and the availability of high-quality data sets (e.g. 2dF, 6dF, SDSS and GAMA surveys) offer a promising avenue for a better understanding on how galaxies form and evolve through time. However, all spectral synthesis studies carried out over the past decade on the basis of these single-fibre spectroscopic surveys lack the necessary spatial resolution to study the radial trends in galaxies. Only recently spatially-resolved data from Integral Field Spectroscopy (IFS) has become available, permitting the study of radial abundance patterns of α-elements in galaxies with unprecedented detail. An innovative aspect of this PhD research project is the use of IFS data for ~600 local Hubble-type galaxies from The Calar Alto Legacy Integral Field spectroscopy Area survey (CALIFA - http://califa.caha.es) to determine the 2D α-element distribution in a spatially resolved pattern. This observational input will be combined with the derived Star-Formation Histories and structural properties of ETGs from CALIFA with the goal of developing new evolutionary diagnostics for ETGs and shedding light into the origin of the α-element enhancement in these systems.